1. Field of the Invention
The present invention relates to a vehicle navigation apparatus which has the GPS positioning system based on a GPS (Global Positioning System) receiver and the self-contained positioning system based primarily on vehicle-velocity sensors and bearing sensors, and displays various navigation information on the basis of the output of either the self-contained positioning system or the GPS positioning system under control of a controller.
2. Prior Art
It is well known that the GPS positioning system is superior in accuracy to the self-contained positioning system. Thus, conventional vehicle navigation apparatuses normally display various navigation information based on position data from the GPS positioning system, and display information from the self-contained positioning system when proper navigation information is not available from the GPS positioning system for various reasons. In this way the navigation information can be supplied from either the GPS positioning system or the self-contained positioning system to the displayer. However, geomagnetism is usually very weak and therefore a geomagnetic sensor as a bearing sensor used in the self-contained positioning system, is quite susceptible to external disturbances. Thus, error results when the geomagnetic sensor is magnetized, the vehicle is magnetized, or when the vehicle runs along a railway or runs across a railway.
The gyro used as a bearing sensor in the self-contained positioning system tends to be affected by external disturbances and results in errors that accumulate. In order to correct the bearing data of the bearing sensor in the self-contained positioning system, it is necessary not only to reset the offset values but also to correct the bearing sensor against some more accurate reference. This is an inconvenient and time consuming task.